Phenoxyanthraquinones are useful as intermediates for the production of dyes as well as other dye intermediates. In the dye industry, phenoxyanthraquinones are usually synthesized by the reaction of a nitro- or halo-anthraquinone with caustic in the presence of excess phenol as both the reactant and solvent.
In the work-up for such processes the phenol melt is diluted with water, the phenoxyanthraquinone is filtered off, and the excess phenol remains in the filtrate and wash. Because of the difficulty in the recovery of the phenol, this process is both expensive and ecologically undesirable. Furthermore, an alkaline reslurry of the product is often needed in order to completely free the product from unreacted excess phenol, and there are substantial yield losses.
This problem has been recently addressed in German OLS No. 2,228,334, in which a water-miscible polar aprotic solvent such as dimethyl formamide, dimethyl sulfoxide, or N-methyl pyrrolidone is used with only a small excess of the phenol and caustic, reacting with the .alpha.-nitro-anthraquinone substrate. In this case the excess phenol is being replaced by an unrecovered and relatively expensive solvent. Recovery of water-miscible, polar, aprotic solvents from an aqueous medium is prohibitively difficult and expensive in terms of time, equipment and energy.
In the art, the treatment of chloro- or nitroanthraquinones with phenol and caustic or with alkali phenoxide to produce phenoxyanthraquinones has only been carried out in the presence of polar solvents such as phenol, alcohol, dimethyl formamide, dimethyl sulfoxide or N-methylpyrrolidone.
An object of this invention is to manufacture phenoxyanthraquinones from chloro- or nitroanthraquinone and alkali phenoxide in high yields of readily-isolable product, without the use of excess phenol, water-miscible alkanols or water-miscible polar aprotic solvents.
A further object of this invention is the substitution, for the solvents of the art, of water-insoluble, non-polar, non-protic solvents which are cheap and readily recoverable from water.